Field of the Invention
The present invention relates to an imaging apparatus, and more particularly, a technique for suppressing an influence of flicker generated under an artificial light source such as a fluorescent lamp.
Description of the Related Art
In recent years, the sensitivity of an imaging apparatus such as a digital camera or a mobile phone camera has been becoming higher. Therefore, a bright image with suppressed blur can be acquired by shooting with a high shutter speed (i.e., with a short exposure time) even under a relatively dark environment such as an indoor environment.
In the case of a fluorescent lamp, which is commonly used as an indoor light source, there occurs flicker known as a phenomenon that illumination light periodically fluctuates due to an influence of a commercial power supply frequency. When shooting with a high shutter speed under a light source that causes such flicker (hereinafter referred to as flickering light source), exposure unevenness and color unevenness may occur in one image, or variations in exposure and color temperature may occur among a plurality of images continuously captured.
To solve such a problem, Japanese Patent Application Laid-Open No. 2006-222935 discusses a technique for detecting a state of flicker of illumination light and adjusting an imaging timing so that the center of an exposure period substantially matches a timing at which a light amount of the illumination light takes a maximal value.
However, in the technique discussed in Japanese Patent Application Laid-Open No. 2006-222935, when a plurality of images is continuously captured, each imaging timing is adjusted based on a phase of the maximal value of the light amount of the illumination light detected before the continuous capturing of the plurality of images is started. Thus, the following problem occurs.
Generally, it has been known that a fluctuation (e.g., a fluctuation of approximately ±0.2 Hz in Japan) occurs in a commercial power supply frequency from a reference frequency. More specifically, a fluctuation, which is approximately two times the fluctuation in the commercial power supply frequency, occurs in a flickering cycle of the flickering light source from a reference flickering cycle. Therefore, when a time elapsed since the flicker has been detected is lengthened, a peak timing of a light amount of the flickering light source obtained from a detection result of the flicker easily deviates from an actual peak timing of the light amount of the flickering light source.
Therefore, in the technique discussed in Japanese Patent Application Laid-Open No. 2006-222935, the later the time when the image is captured in the capturing of the plurality of images is, the more easily the peak timing obtained from the detection result deviates from the actual peak timing, and the more difficult it becomes to suppress an influence of the flicker.